The prior art includes cylinders for plating and other uses, wherein a spiral rib is utilized to push work pieces from an inlet to an outlet. Also known in the prior art is rotation of a cylinder in opposite directions, with the work pieces being plated in one direction of rotation, and the work pieces caught in a side pocket of the cylinder when the latter rotated in an opposite direction for discharge through a door.
However, the prior art fails to disclose a plurality of serially disposed cylinders, with the outlet of one communicating with the inlet of a succeeding one, in combination with spiral ribs adapted to feed work pieces into a cylinder and hold them there for treatment when the cylinder is rotated in one direction, and further adapted to discharge the work pieces from said cylinder and through the outlet thereof and into the inlet of a succeeding cylinder when the first named cylinder is rotated in an opposite direction.